LOL - I bought a Sig Classic and wanted to go full on with putting on the MOE trigger Guard. Much to my surprise when I got it, it was 1/4" too long!
Well, 60 minutes with a bunch of tools, and it fits now. LOL.
1. Check to make sure it's unloaded. Unload if so.
2. Separate upper and lower
3. Remove grip.
d. Remove old guard.
5. Place magpul guard and screw in front screw until the guard is placed, but don't snug it as you must remove it soon.
VI. Mark the back of the magpul guard with a razor blade as to where it lines up flush with the back of the trigger guard housing. It must be flush or the grip won't go back on.
7. Cut the back off with a saw.
8. Cut the ears on the back side side forward until they clear the tang.
8. Plane the top of the guard so that when the rear is pressed into the guard housing, the top of the magpul trigger guard forms a continuous line with the inside of the tang.
9. This will put the remainder of the guard exactly centered around the hole for the pin. You can't afford to have it cocked off to one side or the other, it must be centered around the rear pin hole or you won't have enough material to be strong enough, and you might punch through the plastic.
10. Using the receiver ear and a drill bit exactly sized to fit in the hole, drill the magpul guard. Have the front screw all the way in. (VERY DANGEROUS) Alernately, clamp it in a jig and use a drill press. Less likely to line up perfect.
11. Drive the pin in and enjoy your new trigger guard.
This was a pain in the ass.
You run a shit tonne of risk if you use your receiver as the guide for the drill bit.